UCC2946

UCC3946

SLUS247F − APRIL 1997 − REVISED NOVEMBER 2007

4

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APPLICATION INFORMATION

The UCCx946 supervisory circuit provides accurate reset and watchdog functions for a variety of

microprocessor applications. The reset circuit prevents the microprocessor from executing code during

undervoltage conditions, typically during power-up and power-down. In order to prevent erratic operation in the

presence of noise, voltage glitches where voltage amplitude and time duration are less than the values specified

in Figure 1 are ignored.

100

40

0

110

120

130

140

150

160

170

180

20

100

60

80

120

180

140

160

200

Figure 1.

OVERDRIVE VOLTAGE WITH RESPECT TO

RESET THRESHOLD

vs

TDELAY − Delay Time − µs

RT Senses Glitch,

RES Goes Low for Reset Period

Glitches

Ignored,

RESB

Remains

High

The watchdog circuit monitors the microprocessor’s activity, if the microprocessor does not toggle WDI during

the programmable watchdog period WDO goes low, alerting the microprocessor’s interrupt of a fault. The WDO

pin is typically connected to the non-maskable input of the microprocessor so that an error recovery routine can

be executed.